PSAT Math : PSAT Mathematics

Study concepts, example questions & explanations for PSAT Math

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Example Questions

Example Question #2 : Graphing An Inequality With A Number Line

\(\displaystyle 2x + 6 > 16\)

Which of the following is a graph for the values of \(\displaystyle x\) defined by the inequality stated above?

Possible Answers:

Ineq11

Ineq12

Ineq13

Ineq15

Ineq14

Correct answer:

Ineq11

Explanation:

Begin by solving for \(\displaystyle x\):

\(\displaystyle 2x > 16-6\)

\(\displaystyle 2x > 10\)

\(\displaystyle x> 5\)

Now, this is represented by drawing an open circle at 6 and graphing upward to infinity:

Ineq11

Example Question #1 : Other Number Line

Gre12

If the tick marks are equally spaced on the number line above, what is the average (arithmetic mean) of x, y, and z?

Possible Answers:

5

7

6

4

8

Correct answer:

6

Explanation:

First, we must find out by how much they are spaced by. It cannot be 1, since 4(4) = 16, which is too great of a step in the positive direction and exceeds the equal-spacing limit. 2 works perfectly, however, as 4(2) equals 8 and fits in line with the equal spacing.

Next, we can find the values of x and y since we are given a value of 6 for the third tick mark. As such, x (6 – 4) and y (6 – 2) are 2 and 4, respectively.

Finally, z is 4 steps away from y, and since each step has a value of 2, 2(4) = 8, plus the value that y is already at, 8 + 4 = 12 (or can simply count).

Finding the average of all 3 values, we get (2 + 4 + 12)/3 = 18/3 = 6.

Example Question #693 : Arithmetic

How many numbers 1 to 250 inclusive are cubes of integers?

Possible Answers:

4\(\displaystyle 4\)

8\(\displaystyle 8\)

7\(\displaystyle 7\)

5\(\displaystyle 5\)

6\(\displaystyle 6\)

Correct answer:

6\(\displaystyle 6\)

Explanation:

The cubes of integers from 1 to 250 are 1, 8, 27,64,125,216.

Example Question #1 : How To Find Value With A Number Line

Numberline_1

Refer to the above number line. Which of the points is most likely the location of the number \(\displaystyle 3.5 - \pi\) ?

Possible Answers:

\(\displaystyle B\)

\(\displaystyle D\)

\(\displaystyle C\)

\(\displaystyle E\)

\(\displaystyle A\)

Correct answer:

\(\displaystyle B\)

Explanation:

\(\displaystyle \pi \approx 3.14\), so \(\displaystyle 3.5 - \pi \approx 3.5 - 3.14 \approx 0.36\)

Therefore, 

\(\displaystyle 0.3 < 3.5 - \pi < 0.4\)

On the number line, \(\displaystyle B\) appears between 0.3 and 0.4 and is the correct choice.

Example Question #1 : Negative Numbers

How many elements of the set \(\displaystyle \left \{ -4, -3, -2, -1 \right \}\) are less than \(\displaystyle \left | - 2 \frac{1}{2} \right |\) ?

Possible Answers:

Three

Four

None

Two

One

Correct answer:

Four

Explanation:

The absolute value of a negative number can be calculated by simply removing the negative symbol. Therefore,

\(\displaystyle \left | - 2 \frac{1}{2} \right | = 2 \frac{1}{2}\)

All four (negative) numbers in the set \(\displaystyle \left \{ -4, -3, -2, -1 \right \}\) are less than this positive number.

Example Question #1 : How To Add Negative Numbers

a, b, c are integers.

abc < 0

ab > 0

bc > 0

Which of the following must be true?

Possible Answers:

b > 0

a > 0

a + b < 0

a – b > 0

ac < 0

Correct answer:

a + b < 0

Explanation:

Let's reductively consider what this data tells us.

Consider each group (a,b,c) as a group of signs.

From abc < 0, we know that the following are possible:

(–, +, +), (+, –, +), (+, +, –), (–, –, –)

From ab > 0, we know that we must eliminate (–, +, +) and (+, –, +)

From bc > 0, we know that we must eliminate (+, +, –)

Therefore, any of our answers must hold for (–, –, –)

This eliminates immediately a > 0, b > 0

Likewise, it eliminates a – b > 0 because we do not know the relative sizes of a and b. This could therefore be positive or negative.

Finally, ac is a product of negatives and is therefore positive. Hence ac < 0 does not hold.

We are left with a + b < 0, which is true, for two negatives added must be negative.

Example Question #131 : Arithmetic

What is \(\displaystyle \frac{-36}{-9}\)?

Possible Answers:

\(\displaystyle -4\)

\(\displaystyle -27\)

\(\displaystyle -(+4)\)

45

\(\displaystyle 4\)

Correct answer:

\(\displaystyle 4\)

Explanation:

A negative number divided by a negative number always results in a positive number. \(\displaystyle 36\) divided by \(\displaystyle 9\) equals \(\displaystyle 4\). Since the answer is positive, the answer cannot be \(\displaystyle -4\) or any other negative number.

Example Question #132 : Arithmetic

Solve for \(\displaystyle x\):

\(\displaystyle 16-4x=x+6\)

Possible Answers:

\(\displaystyle -\frac{18}{5}\)

\(\displaystyle -\frac{1}{2}\)

\(\displaystyle \frac{1}{2}\)

\(\displaystyle -2\)

\(\displaystyle 2\)

Correct answer:

\(\displaystyle 2\)

Explanation:

Begin by isolating your variable.

Subtract \(\displaystyle x\) from both sides:

\(\displaystyle 16-4x-x=6\), or \(\displaystyle 16-5x=6\)

Next, subtract \(\displaystyle 16\) from both sides:

\(\displaystyle -5x=6-16\), or \(\displaystyle -5x=-10\)

Then, divide both sides by \(\displaystyle -5\):

\(\displaystyle x=\frac{-10}{-5}\)

Recall that division of a negative by a negative gives you a positive, therefore:

\(\displaystyle x=\frac{10}{5}\) or \(\displaystyle x=2\)

Example Question #2 : How To Add / Subtract / Multiply / Divide Negative Numbers

If \(\displaystyle ab\) is a positive number, and \(\displaystyle -3b\) is also a positive number, what is a possible value for \(\displaystyle a\)?

Possible Answers:

\(\displaystyle 2\)

\(\displaystyle 1\)

\(\displaystyle \frac{1}{2}\)

\(\displaystyle 0\)

\(\displaystyle -1\)

Correct answer:

\(\displaystyle -1\)

Explanation:

Because \dpi{100} \small -3b\(\displaystyle \dpi{100} \small -3b\) is positive, \dpi{100} \small b\(\displaystyle \dpi{100} \small b\) must be negative since the product of two negative numbers is positive.

Because \dpi{100} \small ab\(\displaystyle \dpi{100} \small ab\) is also positive, \dpi{100} \small a\(\displaystyle \dpi{100} \small a\) must also be negative in order to produce a prositive product.

To check you answer, you can try plugging in any negative number for \dpi{100} \small a\(\displaystyle \dpi{100} \small a\).

Example Question #21 : Integers

\(\displaystyle a\)\(\displaystyle b\), and \(\displaystyle c\) are all negative odd integers. Which of the following three expressions must be positive?

I) \(\displaystyle a^{b+c}\)

II) \(\displaystyle a^{b-c}\)

III) \(\displaystyle a^{c-b}\)

Possible Answers:

III only

II only

None of these

I only

All of these

Correct answer:

All of these

Explanation:

A negative integer raised to an integer power is positive if and only if the absolute value of the exponent is even. Since the sum or difference of two odd integers is always an even integer, this is the case in all three expressions. The correct response is all of these.

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